Anhydrous hydrogen fluoride is widely used as a catalyst in the petrochemical industry. It is particularly effective as alkylation catalyst, such as in the production of high-octane gasoline via isoalkane-olefin alkylation. Similarly, detergent alkylates are produced by alkylating aromatic compounds, such as benzene. These technologies have achieved significant application in industry. At the same time, because of the volatility of hydrogen fluoride (HF; boiling point of about 19.6° C.), the environmental and health dangers posed by accidental release from industrial reactors or storage tanks is increasingly unacceptable. To solve this problem, industry has reverted either to the use of sulfuric acid, a less suitable but also less volatile alkylation catalyst, or has operated in a manner that decreases or minimizes the volatility of hydrogen fluoride.
For example, U.S. Pat. No. 5,073,674 discloses the utility of liquid onium polyhydrogen fluoride complexes, containing about 70% to 95% by weight of hydrogen fluoride, as alkylation catalysts. These liquid catalysts, which are not polymer-based, typically have a relatively low molecular weight, optionally contain an additional Lewis acid halide or strong Bronstead acid co-catalyst.
Certain polyhydrogen fluoride complexes, such as polyhydrogen fluoride complexes of pyridine and its derivatives, are liquids which are used as fluorinating agents. For example, anhydrous hydrogen fluoride in the presence of pyridine has been used for fluorinating steroids (R. R. Hirschmann et al., J. Am. Chem. Soc., 1956, 78, 4956). The 30% pyridine-70% hydrogen fluoride system (PPHF) was found to be particularly useful for this reaction (C. G. Bergstrom et al., J. Org. Chem., 1963, 28, 2633) and subsequently was developed (Olah et al., J. Org. Chem., 1979, 44, 3872, and references cited therein) as a general fluorinating agent. The PPHF reagent and subsequently developed related reagents (T. Fukuhara et al., Nippon Kagaku Kaish., 1985, p. 1951) are, however, only suitable as convenient fluorinating agents and are not catalysts for alkylation.
Solid poly-4-vinylpyridinium polyhydrogen fluoride has also previously been utilized for fluorination (Olah et al., Synthesis, 1993, p. 693). This solid fluorination agent, which contains only 35% to 60% hydrogen fluoride by weight is not effective as an alkylation catalyst. Acidic metal hydrogen fluorides, such as those of the type M+HF2−, as well as most other salts of hydrogen fluoride, also fail to catalyze the alkylation of hydrocarbons.